The Other section of the Store and Inventory contains collection assemblers, items for entering paid locations, and sticker duplicates.
The assemblers are used in the Collections window, and the items for entering locations are spent on playing in paid and event locations.
You can get them as rewards for quests, collections, and game events, in gifts and monster treasuries, and for completing locations and mini-games.
Sticker duplicates can be received as a gift from a friend or found in sticker chests during the Sticker Fair and the Festival of Memories events.